U.S. patent number 6,629,645 [Application Number 10/062,844] was granted by the patent office on 2003-10-07 for water mixing valve apparatus.
This patent grant is currently assigned to Aqualisa Products Limited. Invention is credited to Micheal John Cox, Daniel James Flicos, Jocelin Langford, Colin Lander Mountford, Paul John Newcombe, Kelvin Paul Towler.
United States Patent |
6,629,645 |
Mountford , et al. |
October 7, 2003 |
Water mixing valve apparatus
Abstract
A mixing valve apparatus including a mixing valve for mixing
water from a cold water inlet and a hot water inlet and supplying
the mixed water to a water outlet, the water inlets and outlets
being for connection to an external water system, a valve servo for
moving the position of the valve, a control system for operating
the valve servo and thereby controlling at least the temperature at
the water outlet, wherein the control system characterises the
external water system in which the mixing valve is connected and
optimizes control of the valve according to the
characterisation.
Inventors: |
Mountford; Colin Lander
(Parkside, GB), Newcombe; Paul John (Redhill,
GB), Towler; Kelvin Paul (Ashford, GB),
Flicos; Daniel James (Essex, GB), Langford;
Jocelin (Cullompton, GB), Cox; Micheal John
(Royston, GB) |
Assignee: |
Aqualisa Products Limited
(Westerham, GB)
|
Family
ID: |
9907791 |
Appl.
No.: |
10/062,844 |
Filed: |
January 30, 2002 |
Foreign Application Priority Data
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|
|
|
|
Jan 30, 2001 [GB] |
|
|
0102356 |
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Current U.S.
Class: |
236/12.12;
236/93B; 236/93R |
Current CPC
Class: |
G05D
23/1393 (20130101) |
Current International
Class: |
G05D
23/13 (20060101); G05D 23/01 (20060101); G05D
023/13 () |
Field of
Search: |
;236/12.12,91R,93R,93B,51,DIG.2 ;4/676,677 ;137/487.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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375 259 |
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2582418 |
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2 143 343 |
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2 235 309 |
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2 268 302 |
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63089909 |
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JP |
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63089910 |
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Apr 1988 |
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JP |
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2150581 |
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4331859 |
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JP |
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WO 98/26339 |
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Jun 1998 |
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WO |
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WO 99/57381 |
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Nov 1999 |
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WO |
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Primary Examiner: Tapolcai; William E.
Assistant Examiner: Ali; Mohammad M.
Attorney, Agent or Firm: Glenn Patent Group Glenn; Michael
A. Wong; Kirk D.
Claims
We claim:
1. A mixing valve apparatus including: a mixing valve for mixing
water from a cold water inlet and a hot water inlet and supplying
the mixed water to a water outlet, the inlets and outlets being for
connection to an external water system; a valve servo for moving
the position of the valve; and a control system for operating the
valve servo and thereby controlling flow from the water outlet;
wherein the control system includes a control loop for use in
operating the valve servo and is arranged and configured to assume,
when the mixing valve is not used only for a very short period of
time, that the conditions of the external water system have not
changed and to jump start the control loop to restore the valve to
its position as previously used.
2. A mixing valve apparatus including: a mixing valve for mixing
water from a cold water inlet and a hot water inlet and supplying
the mixed water to a water outlet, the water inlets and outlets
being for connection to an external water system; a valve servo for
moving the position of the valve; a control system for operating
the valve servo and thereby controlling at least the temperature at
the water outlet; wherein the control system is arranged and
configured to provide respective characterizations for a plurality
of external water systems, each characterisation providing an
indication of outlet water temperature for mixing valve position on
the basis of inlet water properties for the respective external
water system, and the control system is arranged and configured to
identify the characterization for the external water system in
which the mixing valve is connected and to optimize control of the
valve according to the characterisation.
3. A mixing valve apparatus according to claim 2 wherein the
characterisation takes account of at least one of inlet water
flows, pressures and temperatures.
4. A mixing valve apparatus according to claim 2 wherein the
characterisation used by the control system may be selected by the
user.
5. A mixing valve apparatus according to claim 2 wherein the
control system automatically determines the characterisation on the
basis of operating conditions of the valve.
6. A mixing valve apparatus according to claim 5 wherein the
operating conditions include the mixed temperature at the outlet
and the position of the mixing valve.
7. A mixing valve apparatus according to claim 5 wherein the
operating conditions include change of position of the mixing valve
with respect to change in the actual mixed water temperature at the
outlet.
8. A mixing valve apparatus according to claim 6 wherein the
operating conditions include the temperature of the input hot
water.
9. A mixing valve apparatus according to claim 2 wherein the
control system determines the characterisation with respect to
time.
10. A mixing valve apparatus according to claim 9 wherein the
control system compensates for dead lag in pipes supplying the
mixing valve inlets according to the time since the mixing valve
was last used.
11. A mixing valve according to claim 2 wherein, upon start up, the
control system makes use of the characterisation to move the valve
to a position predicted to produce the required temperature at the
water outlet.
12. A mixing valve apparatus according to claim 2 wherein, when the
mixing valve is not used only for a very short period of time, the
control system assumes that the conditions of the water system have
not changed and jump starts a start up control loop to restore the
valve to its position as previously used.
13. A mixing valve apparatus including: a mixing valve for variably
mixing hot and cold water, a valve servo for moving the mixing
valve; a control system for operating the valve servo so as to
provide a desired mixed water temperature; and a control panel
remote from the mixing valve and valve servo for providing a
control signal to the control system to select the desired
temperature; wherein the control system includes a maximum
temperature selector by which a user may specify a maximum mixed
water temperature selectable by the control panel; and wherein the
control panel includes a display of selectable mixed water
temperatures, the display only showing temperatures up to the
selected maximum mixed water temperature and the display has a
fixed predetermined extent, the scale of which is varied according
to the selected maximum mixed water temperature.
14. A mixing valve apparatus according to claim 13 wherein the
maximum temperature selector is provided proximate the valve and
the valve servo.
15. A mixing valve apparatus according to claim 13 wherein the
control panel includes a member movable between two predetermined
end positions to select the mixed water temperature and wherein one
of the predetermined end positions selects the selected maximum
mixed water temperature and the scale of selectable mixed water
temperatures between the two predetermined end positions is
adjusted according to the selected maximum mixed water
temperature.
16. A mixing valve apparatus including: a cold water inlet and a
hot water inlet; a mixing valve for mixing water received at the
cold water inlet and the hot water inlet and supplying the mixed
water to a water outlet, the inlets and outlets being for
connection to al external water system; a valve servo for moving
the position of the valve; and a control system for operating the
valve servo and thereby controlling flow from the water outlet, the
control system including a temperature sensor for providing an
indication of the temperature at the water outlet and a control
loop for comparing the desired temperature with that provided by
the temperature sensor so as to operate the valve servo; wherein
the control system additionally includes a transient detector for
determining from the temperature indicated by the temperature
sensor transients in the properties of the water received at the
cold water inlet and the hot water inlet and overriding the control
loop to control the valve servo in the event of a transient.
17. A mixing valve according to claim 16 wherein, in the event of a
transient the valve servo is controlled to rapidly reduce the
supply of water from the hot water inlet to the water outlet to
substantially zero.
18. A mixing valve apparatus according to claim 16 the transient
detector continuously monitors the rate of change in temperature
indicated by the temperature sensor.
19. A mixing valve apparatus according to claim 18 where the
transient detector predicts the actual temperature at the water
outlet from the rate of change in temperature indicated by the
temperature sensor and the time constant of the temperature
sensor.
20. A mixing valve apparatus including: a mixing valve for mixing
water from a cold water inlet and a hot water inlet and supplying
the mixed water to a water outlet, the inlets and outlets being for
connection to an external water system; a valve servo for moving
the position of the valve; and a control system for operating the
valve servo and thereby controlling flow from the water outlet;
wherein the control system includes an error detection circuit for
detecting at least one of the following: failure of a temperature
sensor providing an indication of the temperature at the outlet;
failure of a selected intermediate maximum temperature for delivery
from the outlet; and disconnection of a control panel for
controlling the control system.
21. A mixing valve apparatus according to claim 20 wherein the
error detection circuit only recognises indications of the
temperature between predetermined limits as valid temperatures and
determines failure of the temperature sensor when the indication of
temperature is outside the predetermined limits.
22. A mixing valve apparatus according to claims 20 wherein the
intermediate maximum temperature is selected using a potentiometer,
the maximum selectable intermediate maximum temperature being
selected with the potentiometer at its maximum resistance and a
fixed resistor being provided in series with the potentiometer such
that higher resistances are detected as errors.
23. A mixing valve according to claim 22 wherein the minimum
temperature selectable as the intermediate maximum temperature
corresponds to a closed circuit such that an unwanted short circuit
fails safe.
24. A mixing valve apparatus according to claim 20 wherein the
error detection circuit regularly checks for valid signals from the
control panel and detects an error when no valid signal is
received.
25. A mixing valve apparatus according to claim 24 wherein, for
analogue control panels, the error detection circuit checks for
valid signal levels, and, for digital control panels, the error
detection circuit checks that the control panel can
communicate.
26. A mixing valve apparatus including: a mixing valve for mixing
water from a cold water inlet and a hot water inlet and supplying
the mixed water to a water outlet, the inlets and outlets being for
connection to an external water system; a valve servo for moving
the position of the valve; and a control system for operating the
valve servo and thereby controlling flow from the water outlet;
wherein the control system stores information relating position of
the valve and valve servo to temperature at the outlet and, upon
start-up, when a desired temperature is selected, initially
operates the valve servo to move the valve to the position stored
for the selected temperature.
27. A mixing valve apparatus including: a mixing valve for variably
mixing hot and cold water; a valve servo for moving the mixing
valve; a control system for connection to a remotely located
control panel and for operating the valve servo so as to provide a
desired mixed water temperature according to the control panel;
wherein the control system includes an input port suitable for
connection selectively to an analogue control panel and a digital
control panel.
28. A mixing valve apparatus according to claim 27 wherein the
input port includes six lines of which two lines are suitable for
analog control signals.
29. A mixing valve apparatus according to claims 27 wherein the
input port includes an input termination circuit.
30. A mixing valve apparatus according to claim 29 wherein the
input termination circuit includes: a fist capacitor between ground
and an input port; a first resistor between the input port and a
digital input; a second resistor between the input port and an
analog input; and a second capacitor between the analog input and
ground; wherein the second resistor has a higher impedance with
respect to the first resistor.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a water mixing valve apparatus
and, more particularly, to improvements in the control system of a
water mixing valve apparatus having a servo controlled mixing
valve.
2. Description of the Related Art
Previously it was known to provide an electronically controlled
mixing valve for mixing hot and cold water to provide outlet water
of a desired temperature. The apparatus was provided with a control
loop having a temperature sensor in the outlet of the mixing valve
so that the mixing valve could be adjusted to provide a desired
outlet temperature. It was also known to provide the mixing valve
apparatus as part of a shower, e.g. for washing.
This known mixing valve apparatus has a problem when it is
installed in a non-linear environment. For instance, where a mixing
valve is installed in a water system having a higher pressure cold
water supply, the first part of movement of the mixing valve will
have little effect in raising the outlet temperature and the outlet
temperature will be very sensitive to movement of the valve in a
later small range.
OBJECTS AND SUMMARY OF THE INVENTION
To overcome this problem, it is possible to adapt the mixing valve
for a particular pressure system, for instance by inserting
restrictors in the inlet pipes. However, the installation of such
restrictors is not a trivial matter and, unless the nature of a
water system is known in advance, it is necessary to use trial and
error to determine the correct restrictor. Furthermore, it is
necessary to produce and stock a selection of different restrictors
for different types of water system.
It is also possible to use a control loop which adjusts dynamically
according to sensed operating conditions. However, this is unduly
complicated and requires the control loop to reconfigure itself
when the valve is moved between different portions of a stable, but
non-linear environment.
According to the present invention, there is provided a mixing
valve apparatus including: a mixing valve for mixing water from a
cold water inlet and a hot water inlet and supplying the mixed
water to a water outlet, the water inlets and outlets being for
connection to an external water system; a valve servo for moving
the position of the valve; a control system for operating the valve
servo and thereby controlling at least the temperature at the water
outlet; wherein the control system characterises he external water
system in which the mixing valve is connected and optimizes control
of the valve according to he characterisation.
In this way, it is not necessary for different mixing valves to be
provided for different installations or to provide additional parts
to adapt the mixing valve for different installations. The control
system can adapt the way it controls the mixing valve according to
the properties of the external water system In particular, for a
given temperature change at a particular point in the temperature
range, the control system can move the mixing valve by a different
amount according to how the external water system has been
characterised. Where the control system uses an outlet temperature
sensor with a control loop, it can optimise control of the valve by
varying, according to the characterisation, the amount of movement
of the valve to correct a difference between actual and desired
temperature as detected by the temperature sensor. In other words,
the control loop in effect employs a gain which varies through the
valves range according to the characterisation.
However, for the particular characterization, appropriate gains are
known for positions throughout the operating range and there is no
need for the system to dynamically change the gain on the basis of
sensed conditions. A respective characterization represents an
entire operating range.
Preferably, the characterisation takes account of at least one of
inlet water flows, pressures and temperatures. This enables the
mixing valve apparatus to be optimised for a wide variety of
external water systems.
The characterisation used by the control system can be selected by
the user, for instance by means of an input selector. In this way,
the user merely preselects the type of external water system in
which the mixing valve apparatus is installed or changes the
selection until an optimum response is observed.
On the other hand, the control system could automatically determine
the characterisation on the basis of operating conditions of the
valve.
In this way, the control system determines the characterisation of
the external water system on the basis of the properties of the
water at the outlet of the mixing valve compared to the controlled
position of the valve to produce those properties.
Hence, the operating conditions may include the mixed temperature
at the outlet and the position of the mixing valve. Furthermore,
they may include the cold water inlet temperature or an estimation
thereof. Similarly, the operating conditions can include a measure
of the change of position of the mixing valve with respect to a
change in the actual mixed water temperature at the outlet.
By additionally considering the cold water inlet temperature, the
control system only requires data relating to two other operating
positions to characterise the external system.
The operating conditions may additionally include the temperature
of the input hot water.
In this way, the control system only requires data relating to one
intermediate position of the valve to characterise the external
system.
Thus, by using the input cold and/or hot water temperatures, the
control system is able to characterise the external system more
quickly and easily.
Preferably the control system is continuously adaptive such that,
should the properties of the external system change, the
characterisation will also change. In other words, the applicable
response or gain for the operating range will change. However, in
addition, the control system may also determine the
characterisation of the external water system with respect to time.
In this way, the control system can predict conditions where the
properties of the external water system change over time. For
instance, the control system could compensate for the temperature
of the hot water inlet decreasing over time as the temperature in a
hot water supply tank decreases. Similarly, the control system
could compensate for dead leg in supply pipes according to time
since the mixing valve was last used and/or changes as the
temperature of a supply pipe comes up to the temperature of the
water it carries.
Preferably, upon stat up, the control system makes use of the
characterisation to move the valve to a position predicted to
produce the required temperature at the water outlet.
Indeed, according to the present invention, there is provided a
mixing valve apparatus including: a mixing valve for mixing water
from a cold water inlet and a hot water inlet and supplying the
mixed water to a water outlet, the inlets and outlets being for
connection to an eternal water system; a valve servo for moving the
position of the valve; and a control system for operating the valve
servo and thereby controlling flow from the water outlet; wherein
the control system stores information relating position of the
valve and valve servo to temperature at the outlet such that, upon
start-up, when a desired temperature is selected the valve servo is
initially operated to move the valve to the position stored for the
selected temperature.
Where the control system uses a temperature sensor in the outlet
together with a control loop, the control system positions the
valve without using the control loop for a short predetermined
period of time. In this way, when the control loop is again used,
the valve position and the actual temperature should be close to
the required position and temperature such that the required
temperature can be reached more quickly and with less oscillation
in temperature.
Often mixing valves will be used in systems which are shut down and
restarted within a short period of time. For instance, in a
domestic shower, the shower may be turned off briefly while the
user is applying soap or shampoo.
Preferably, when the mixing valve is not used only for a very short
period of time, the control system assumes that the conditions of
the water system have not changed and jump starts a start up
control loop to restore the valve to its position as previously
used.
According to the present invention, there is provided a mixing
valve apparatus including: a mixing valve for mixing water from a
cold water inlet and a hot water inlet and supplying the mixed
water to a water outlet, the inlets and outlets being for
connection to an external water system; a valve servo for moving
the position of the valve; and a control system for operating the
valve servo and thereby controlling flow from the water outlet,
wherein when the mixing valve is not used only for a very short
period of time, the control system assumes that the conditions of
the external water system have not changed and jump starts a
start-up control loop to restore the valve to its position as
previously used.
In other words, irrespective of any other control systems or
control loops, the valve may be driven directly to the position it
had when it was last used.
In this way, the valve is moved directly to a position suitable for
producing the desired outlet conditions. This is particularly
useful for a mixing valve used to control both flow and
temperature. Furthermore, by jump stating the start up control loop
such that the control loop is at first ignored, the system avoids
undue oscillations and time delay as the control loop brings he
valve to its required position. The control loop may be activated
once the valve has reached the required position.
In previous mixing valves for controlling the temperature of a
water outlet, it was known to provide an intermediate maximum
temperature stop so as to prevent use of the outlet above a
preselected temperature. However, there is a problem that these
stops can inadvertently be overridden.
According to the present invention, there is provided a mixing
valve apparatus including: a mixing valve for variably mixing hot
and cold water; a valve servo for moving the mixing valve; a
control system for operating the valve servo so as to provide a
desired mixed water temperature; and a control panel remote from
the mixing valve and valve servo for providing a control signal to
the control system to select the desired temperature; wherein the
control system includes a maximum temperature selector by which a
user may specify a maximum mixed water temperature selectable by
the control panel; and wherein the control panel includes a display
of selectable mixed water temperatures, the display only showing
temperatures up to the selected maximum mixed water temperature and
the display has a fixed predetermined extent, the scale of which is
varied according to the selected maximum mixed water
temperature.
In this way, users are only presented with available mixed water
temperatures and, unlike previous systems where higher unselectable
temperatures are displayed, no motivation is provided to select
higher temperatures. Furthermore, the scale makes fill use of the
available display and, furthermore, for low maximum temperatures,
the scale can be increased to show changes in temperature with
greater accuracy.
Preferably, the maximum temperature selector is provided proximate
the mixing valve and the valve servo.
Since the control panel is provided remote from the mixing valve
and the valve servo and since the maximum temperature selector is
provided proximate the mixing valve and valve servo, it is not
possible for a user to inadvertently change the temperature
specified by the maximum temperature selector. Hence, a user may
freely select temperatures using the control panel without any
danger of selecting a temperature beyond that specified by the
maximum temperature selector.
Despite this, by accessing the mixing valve and valve servo, it is
still possible to provide a maximum temperature selector which
easily adjusts the selected maximum temperature according to
requirements.
The control panel may include a member movable between two
predetermined end positions to select the mixed water temperature,
one of the predetermined end positions selecting the selected
maximum mixed water temperature and the scale of selectable mixed
water temperatures between the two predetermined end positions
being adjusted according to the selected maximum mixed water
temperature.
In this way, for lower maximum temperatures, the full range of
movement is still possible, such that temperatures may be selected
with greater accuracy. This is applicable to sliders and also
rotatable control knobs.
It should be noted that it would also be possible to provide a
similar minimum temperature selector and to change the scales of
the display and/or control member accordingly.
In previous systems where a flow of water is controlled by an
electrically operable mixing valve, there has been a problem when
power failures occur. In particular, without electrical power for
the mixing valve, it remains in its open position. It has been
proposed to provide mechanical actuators to allow the valve to be
closed manually. However, these are inconvenient to use,
particularly when the mixing valve is installed in a shower and,
hence, the user is wet.
According to the present invention, there is provided a mixing
valve apparatus including: a mixing valve for controlling flow of
water; a valve servo for moving the mixing valve; a control system
for operating the valve servo to move the mix valve; an electrical
power input for receiving power for the valve servo and control
system; and an electrical energy store for powering tee valve servo
and control system in the event that no power is received by the
electrical power input, in such event, the control system operating
the valve servo to move the valve to a position of no flow.
Hence, in the event of a power failure, the electrical energy store
provides power to close the valve and shut off supply of water from
the outlet.
This is particularly useful for valves having and preferably the
apparatus has a valve member with apertures for hot and cold water
and movable between a position of no flow and positions of mixed
flow between maximum hot and maximum cold.
For these valves, a power failure may result also in changes in the
external system providing the hot and cold water, such that the
water outlet produces water which is unacceptably hot or cold. By
means of the electrical energy store, it is possible safely to shut
off the valve.
The valve member may provide a no flow position at two positions,
one adjacent the maximum cold position and one adjacent the maximum
hot position.
Although, in normal use, the valve member might be moved to the no
flow position adjacent the maximum cold position, in the event that
no power is received by the electrical power unit, the control
system preferably operates the valve servo to move the valve member
to the nearest of the two no flow positions.
In this way, the valve is moved to its off position most quickly
and with the least amount of energy.
Preferably, in the event that no power is received by the
electrical power unit, the control system switches off power to
unnecessary components of the mixing valve apparatus so as to
conserve power.
Thus, the control system only provides power to components
essential for operating the mixing valve. For instance, any
illumination of an associated control panel could be turned
off.
In this way, depending on the size of the electrical energy store,
it can be possible to continue operation of the mixing valve
apparatus for some time before the valve servo moves the valve to a
position of no flow.
In this respect, the control system could switch off power to any
control loop for the valve on the basis that the operating
conditions will not change over the short period of time following
the power failure.
Preferably, the electrical energy store is a capacitor. This
provides a longer service life than a battery and, also, allows
energy storage at a higher voltage.
While power is received by the electrical power input, the
capacitor may be charged to the highest possible safe voltage, for
instance, at least 40 volts or a legislated maximum voltage, such
as 42.4 volts.
In the event that no power is received by the electrical power
input, the control system may determine the remaining electrical
energy stored in the electrical energy store and operate the valve
servo to move the valve to the position of no flow when the
remaining electrical energy equals that needed to move the valve to
the position of no flow.
In this way, for power failures of relatively short duration, it
would be possible to continue operation of the mixing valve
apparatus without interruption.
The valve servo may comprise a stepper motor. In this case, the
control system preferably operates the stepper motor by half steps
when power is received by the electrical power input and by whole
steps in the event that no power is received by the electrical
power input.
Preferably, in the event that no power is received by the
electrical power input, the control system operates the valve servo
to move the mixing valve to a position of no flow using the optimum
servo trajectory resulting in the use of minimum power.
It will be appreciated that it is possible to operate a servo in
many ways. In normal operation, the servo is usually operated to
provide an optimum response by moving the valve quickly to a
desired position Depending on the characteristics of the servo, it
will also be possible to operate the servo in such a manner that it
moves to a desired position with minimum use of power. By moving
the mixing valve to a position of no flow using a minimum amount of
power, the size of the electrical energy store may be minimised or
the time during which the mixing valve apparatus may continue to
operate during a power failure may be maximised.
In known electrically operated mixing valves, there is a problem of
providing very accurate control of the mixing valve due to backlash
in the gear train transferring motion to the mixing valve.
According to the present invention, there is provided a mixing
valve apparatus including: a mixing valve for mixing water from a
cold water inlet and a hot water inlet and supplying the mixed
water to a water outlet; a stepper motor; a gear train for
transferring motion of the stepper motor to the mixing valve; a
detector for detecting at least one predetermined position of the
mixing valve; and a control system for sequentially operating the
stepper motor to move the mixing valve in one direction past said
at least one predetermined position and in an opposite direction
past said at least one predetermined position, thereby to determine
with reference to the detector the back lash in the gear train.
In this way, when the control system is required to move the mixing
valve in a direction opposite to the direction in which it was last
moved, it can operate the stepper motor by an additional amount
equal to the backlash in the gear train so as to move the mixing
valve accurately to the required position. This can significantly
improve the accuracy of the control system.
The control system is preferably responsive to a control signal to
move the mixing valve to a position indicated by the control
signal, the control system operating the stepper motor accordingly,
taking account of the backlash in the gear train.
Thus the control signal could be derived from a temperature sensor
in the water outlet for controlling the water outlet temperature.
By correcting for the backlash in the gear train, it is then
possible to move the mixing valve accurately as part of the control
loop and make small changes in mixing valve position to more
accurately control the outlet temperature.
Of course, the control signal may also be derived from a demand
temperature input by a user.
In previous mixing valves, there has been a problem when the mixing
valve is not operated for long periods of time. Due to stiction and
such like between resilient seals and their sealing surfaces, undue
strain can be placed on the valve servo and operating mechanism.
Also additional wear and strain is placed on the resilient seals
themselves.
According to the present invention, there is provided a mixing
valve apparatus including: a valve having at least one sealing
surface against which at least one resilient seal presses; a valve
servo for moving the valve; a control system for operating the
valve servo in response to a control signal; wherein in the absence
of a control signal to move the valve within a predetermined
period, the control system operates the valve automatically so as
to keep the resilient seal from sticking to the sealing
surface.
Preferably, the predetermined period is at least 24 hours. This is
particularly useful for mixing valves used in showers. Showers are
often used regularly at the same time each day. Hence, the control
system will operate the valve servo if the shower is not operated
by the user at this regular time.
Movement of the valve need only be sufficient to prevent the
resilient seals from sticking to the sealing surfaces. Preferably,
the valve is arranged such that it can be moved sufficiently to
move the resilient seals relative to their sealing surfaces without
the valve providing flow therethrough.
In this way, the external system in which the valve is installed
will not be affected in any way by the operation.
Where a mixing valve is controlled by means of a control loop
having a sensor in the outlet, it is often necessary to have a
damped response. For example, where the control loop is used to
maintain a particular temperature of water at the outlet, it is
undesirable for the control loop to be undamped, since the system
will unduly oscillate when moving to a new temperature and will
overreact to changes in temperature resulting from minor changes to
the inlet streams, for instance due to other usage on the same
water supply. On the other hand, in certain circumstances, for
instance a cold water supply failures it is extremely important
that the system reacts quickly, for instance to shut off the water
flow before a user becomes scalded.
According to the present invention, there is provided a mixing
valve apparatus including: a mixing valve for mixing water from a
cold water inlet and a hot water inlet and supplying the mixed
water to a water outlet, the inlets and outlets being for
connection to an external water system; a valve servo for moving
the position of the valve; and a control system for operating the
valve servo and thereby controlling flow from the water outlet, the
control system including a temperature sensor for providing an
indication of the temperature at the water outlet and a control
loop for comparing the desired temperature with that provided by
the temperature sensor so as to operate the valve servo; wherein
the control system additionally includes a transient detector for
determining transients in the water flow from the temperature
indicated by the temperature sensor and overriding the control loop
to control the valve servo in the event of a transient.
In this way, during normal usage, the control loop may provide the
desired damped response for controlling the outlet temperature.
However, when a transient is detected by the transient detector,
the control loop can be overridden so as to allow the control
system to take immediate action in view of the detected temperature
changes.
In other words, the normal control loop no longer has control over
movement of the valve and the transient detector causes the valve
to be moved rapidly to a safe position.
It will be appreciated that the effect of damping is often provided
by the temperature sensor itself, since, for normal use, this need
only have a relatively slow response time.
Preferably, in the event of a transient the valve servo is
controlled to rapidly reduce the supply of water from the hot water
inlet to the water outlet to substantially zero.
Preferably, the transient detector continuously monitors the rate
of change in temperature indicated by the temperature sensor.
In this way, the transient detector may predict the actual
temperature at the water outlet from the rate of change in
temperature indicated by the temperature sensor and the time
constant of the temperature sensor.
In other words, knowing the time constant of the temperature sensor
and, hence, the limit to which it can show a rate of change in
temperature, when the temperature sensor indicates a rate of change
at that limit, the transient detector can predict an actual rate of
change which is much greater.
In this way, the transient detector can predict an unacceptable
rise in temperature such that the control system can take
appropriate action.
Significant problems can arise with previous electronically
controlled mixing valves due to faults in the system. For instance,
failure of a temperature sensor can cause the mixing valve to be
moved to a position producing an unacceptably high or low
temperature.
According to the present invention, there is provided a mixing
valve apparatus including: a mixing valve for mixing water from a
cold water inlet and a hot water inlet and supplying the mixed
water to a water outlet, the inlets and outlets being for
connection to an external water system; a valve servo for moving
the position of the valve; and a control system for operating the
valve servo and thereby controlling flow from the water outlet;
wherein the control system includes an error detection circuit for
detecting at least one of the following: failure of a temperature
sensor providing an indication of the temperature at the outlet;
failure of a selected intermediate maximum temperature for delivery
from the outlet; and disconnection of a control panel for
controlling the control system.
In this way, the mixing valve apparatus is able to operate safely
despite any faults which may occur.
Upon detecting an error, the control system can operate the mixing
valve in a fail-safe mode, for instance moving the valve to full
cold, to a safe intermediate temperature or shutting off the flow
of water from the outlet.
Preferably, the error detection circuit only recognises indications
of the temperature between predetermined limits as valid
temperatures and determines failure of the temperature sensor when
the indication temperature is outside the predetermined limits.
The temperature limits may be set such that if the temperature
sensor goes open circuit or closed circuit, the error detection
circuit determines an error. This prevents the control system
driving the valve to full cold or full hot in response to an
erroneous signal indicating maximum or minimum temperature.
The intermediate maximum temperature may be selected using a
potentiometer, the maximum selectable intermediate maximum
temperature being selected with the potentiometer at its maximum
resistance and a fixed resistor being provided in series with the
potentiometer such that higher resistances are detected as
errors.
In this way, if the potentiometer for selecting the intermediate
maximum temperature becomes disconnected, the open circuit is not
recognised as a high intermediate maximum temperature and the
control system takes appropriate action; for instance issuing a
warning and shutting off the valve or using an internal default
intermediate maximum temperature.
Preferably, the sum temperature selectable as the intermediate
maximum temperature corresponds to a closed circuit such that an
unwanted short circuit fails safe.
In particular, if a short circuit occurs, the system reacts to this
as if the minimum temperature has been selected as the intermediate
maximum temperature. Hence, such a failure will not cause scalding
of the user.
Preferably, the error detection circuit regularly checks for valid
signals from the control panel and detects an error when no valid
signal is received.
For analogue control panels, the error detection circuit checks for
valid signal levels, and, for digital control panels, the error
detection circuit checks that the control panel can
communicate.
In this way, should the control panel fail or become disconnected,
the control system can take appropriate action, for instance
shutting off the valve.
According to the present invention, there is provided a mixing
valve apparatus including: a mixing valve for mixing water from a
cold water inlet and a hot water inlet and supplying the mixed
water to a water outlet, the inlets and outlets being for
connection to an external water system; a valve servo for moving
the position of the valve; and a control system for operating the
valve servo and thereby controlling flow from the water outlet;
wherein the control system stores information relating position of
the valve and valve servo to temperature at the outlet such that,
upon start-up, when a desired temperature is selected the valve
servo is initially operated to move the valve to the position
stored for the selected temperature.
According to the present invention, there is provided a mixing
valve apparatus including: a mixing valve for variably mixing hot
and cold water; a valve servo for moving the mixing valve; a
control system for connection to a remotely located control panel
and for operating the valve servo so as to provide a desired mixed
water temperature according to the control panel; wherein the
control system includes an input port suitable for connection
selectively to an analogue control panel and a digital control
panel.
Preferably, the input port includes six lines of which two lines
are suitable for analog control signals.
Preferably the input port includes an input termination
circuit.
Preferably the input termination circuit includes; a first
capacitor between ground and an input port; a first resistor
between the input port and a digital input; a second resistor
between the input port and au analog input; and a second capacitor
between the analog input and ground; wherein the second resistor
has a higher impedance with respect to the first resistor.
According to the present invention, there is provided a method of
communicating with a mixing valve apparatus having a mixing valve
for variably mixing hot and cold water, a valve servo for moving
the mixing valve and a control system with a digital interface
allowing input of a digital signal so as to cause the control
system to operate the valve servo and provide a desired nixed water
temperature, the method comprising: providing a control message of
8 bits having, in order, a destination address byte, a source
address byte, a command number byte, three payload bytes and two
CRC bytes.
Preferably, the command number has at least six values representing
respectively report system status, switch valve on or off, set
temperature, switch pump on or off, report temperature and report
pump status.
It should be noted that any of the features discussed above can be
combined together in any combination in a water mixing valve
apparatus so as to give rise to a mixing valve apparatus having the
corresponding advantages.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates schematically a remote controlled water mixing
valve apparatus embodying the present invention;
FIG. 2 illustrates a cross section through a valve suitable for use
with the present invention;
FIG. 3 illustrates a valve member for use in the valve of FIG.
2;
FIG. 4 illustrates typical profiles for the mixing of hot and cold
water supplies;
FIG. 5 illustrates schematically a control loop for the control
system of FIG. 1;
FIG. 6 illustrates the profile for an external water system as
split into temperature bands;
FIGS. 7(a) and (b) illustrate embodiments of control panels;
and
FIG. 8 illustrates a control system using an additional electrical
energy store.
FIG. 9 illustrates examples of temperature versus valve
position;
FIG. 10 illustrates a graph of gradients of the curves of FIG.
9;
FIG. 11 represents the maximum gradient curve for FIGS. 9 and 10;
and
FIG. 12 illustrates au input termination circuit.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will be more clearly understood from the following
description, given by way of example only, with reference to the
accompanying drawings.
As illustrated in FIG 1, the water mixing apparatus includes a
mixing valve 2 which is operated by a valve servo 4 under the
control of a control system 6. The control system 6 receives a
control signal from a remote control panel 8.
As illustrated, the control panel 8 is connected to the control
system 6 by means of a cable or wire 10. However, any appropriate
communication may be provided between the control panel 8 and
control system 6, including wireless systems. The control panel 8
is at least able to indicate in the control signal a desired water
outlet temperature. However, it may also indicate other properties
to the control system 6 in the control signal. Furthermore, a
signal may be transmitted from the control system 6 to the control
panel 8 in order to display information on the control panel 8.
The mixing valve 2 includes at least two inlets 12 and 14. These
inlets 12, 14 are respectively for transfer fluid of different
properties to the mixing valve 2. Hence, inlet 12 may provide a
flow of cold water to the mixing valve 2 and inlet 14 may provide a
flow of hot water to the mixing valve 2.
Fluid mixed by the mixing valve 2 flows out of the mixing valve 2
via an outlet 16.
As mentioned above, the mixing valve 2 is operated by means of a
valve servo 4, for example a stepper motor. The valve servo 4 is
controlled by the control system 6 so as to move the mixing valve 2
to a position providing the desired mixed output flow through
outlet 16.
FIG. 1 illustrates a temperature sensor 18 located in the mixed
flow of fluid so as to detect the temperature of mixed fluid. As
illustrated, the temperature sensor 18 is positioned in the outlet
16. However, the temperature sensor 18 can also be positioned in
the mixing chamber of the mixing valve 2 provided that it is at a
position which will give a correct representation of the mixed
outlet temperature.
By means of the temperature sensor 18, the control system 6 can
operate the valve servo 4 so as to move the mixing valve 2 to a
position providing a desired output temperature.
FIG. 2 illustrates a cross-section through a preferred mixing valve
2 for use in the apparatus of FIG. 1 The mixing valve 2 includes a
valve member 20 as illustrated in FIG. 3.
Inlets 12,14 include cup seals 22,24 which seal against the face 26
of valve member 20.
As illustrated in FIG. 3, valve member 20 includes tapered
apertures 28. In this way, by rotating the valve member 20 relative
to the cup seals 22,24 of the inlets 12,14, one of the inlets is
opened fully to the mixing chamber of the mixing valve 2 and then,
as flow from that inlet is progressively reduced, flow from the
other inlet is progressively increased. In this way, any desired
mix from the inlets 12,14 can be obtained.
As illustrated in FIG. 2, the valve member 20 may be rotated by a
shaft 30 extending through the mixing valve 2. The shaft 30 is
rotated by the valve servo 4 either directly or by means of a gear
train. The gear train may be provided separately or may be housed
internally of the valve servo 4.
It should be appreciated that other arrangements of servo operated
mixing valves are also possible.
Where the mixing valve 2 is used in a system having equal pressure
and flow characteristics for the supply to both inlets 12 and 14,
it is possible to provide a linear mixing response with respect to
movement of the valve. For mixing hot and cold fluids, this is
illustrated by the solid line in the graph of FIG. 4.
In practice, the system will have different pressure and flow
characteristics on different supply pipes. In particular, for a
domestic water supply, where hot and cold water is supplied to the
mixing valve 2, the cold water may be of higher pressure than the
hot water or the hot water of higher pressure than the cold water.
These two situations are illustrated in FIG. 4. In particular,
where the hot water is of higher pressure than the cold water, the
mixed outlet temperature will follow the characteristic illustrated
by the broken line of FIG. 4 with reference A. On the other hand,
if the cold water is of higher pressure than the hot water, the
outlet temperature will follow the characteristic illustrated by
the broken line of FIG. 4 having reference B. Thus, it will be
appreciated that the system in which the mixing valve is installed
can be classed as having a particular characterisation.
For the example given above, the water system can most simply be
characterised as having one of three characterisations, namely a
high pressure hot water system, an equal pressure system or a high
pressure cold water system.
Having recognised the above it is now proposed to provide the
control system with a user operable switch 32 allowing selection of
the appropriate characterisation for the system in which the mixing
valve apparatus is installed. In one arrangement, the switch 32
could be provided with only three states corresponding respectively
to the three basic characterisations Equally, in another
arrangement, it could be provided with additional states for
intermediate characterisations. Alternatively, the switch could
allow continuous selection of characterisations within a
predetermined range.
On the basis of the characterisation, the control system 6 is able
to operate the valve servo 4 in a manner to optimise the response
of the system, thereby achieving higher response times and a more
stable control. In particular, the control system 6 adjusts the
position of the valve 2 at a rate appropriate with the actual
change in mixing resulting from a change in position. In this way,
the control system 6 can make the response of the control as fast
as possible and also minimise overshoot.
In this respect, it will be appreciated that where there is a
control loop, for instance as provided by the temperature sensor 18
of FIG. 1, the control system 6 is able to select any desired
output mix even without knowing the characterisation of the
external system. However, by knowing the characterisation of the
external system, the control system 6 can operate the valve servo 4
to move the mixing valve 2 more or less than would otherwise be
expected for a given change of mix at the outlet. Thus, for
example, for the characteristic A in FIG. 4, the control system 6
would operate the valve servo 4 to move the valve 2 less for
temperatures at the lower end of the temperature range than for
temperatures at the higher end of the temperature range. In other
words, the gain varies with valve position and this information is
used to optimize the control loop.
Hence, an appropriate characterization defining the relationship
between valve position and outlet temperature for at least the
usual operating range is chosen. This is then used to obtain any
desired outlet temperature. Control loop gain need not be varied
dynamically during movement of the valve between different
positions since the characterization of the external system is
sufficient for optimising control over at least the usual operating
range
Instead of or in addition to the user selection switch 32, it is
possible to provide a control system 6 which automatically
determines the characteristics of the system in which the mixing
valve apparatus is installed. In particular, the control system 6
can automatically choose one of a predetermined number of different
characterizations. It can compare how much it instructs the valve
servo 4 to move the mixing valve 2 with respect to detected changes
in mix, for instance changes in the temperature detected by the
temperature sensor 18. As a result, the control system can
alternatively build up a profile of the mix response and, hence,
control the mixing valve 2 more effectively. Once again, however,
the resulting profile forms a characterization representing the
operating range, thereby allowing the valve to be moved freely
between different positions and outlet temperatures without the
need to dynamically adjust control loop gain for each new
position.
Preferably, the control system 6 monitors the response curve on a
continuous basis such that, if the response changes over time, the
control system 6 changes its characterisation of the external
system and changes its control of the valve servo 4 accordingly.
Thus, the control system 6 may undergo a continuous learning
process.
For a general system, in order to have a complete and accurate
profile for the characterisation, the control system 6 must operate
the mixing valve 2 through the complete range of positions and
resulting mixes. In this way, the control system 6 can build up any
profile, even a profile of irregular form which does not correspond
to any of the profiles illustrated in FIG. 4.
In some circumstances, it may be undesirable for the valve to be
moved through its complete range because it will take time and
because a user may only want the mixing valve to operate with a
single predetermined mix.
However, by assuming that the characterisation can be approximated
by one of a predetermined selection of profiles such as those
illustrated in FIG. 4, it is possible to more quickly and easily
determine an appropriate characterisation. In particular, by
establishing at least 3 points with regard to valve position and
mix properties, it is possible to estimate an appropriate profile
and to establish the required characteristics for the control
system.
For mixing hot and cold fluids, it is proposed to measure or at
least estimate the input cold temperature. This then gives the
control system 6 the lowest point of the profile as illustrated in
FIG. 4 and allows the control system 6 to predict an appropriate
characterisation based on only two other points on the
temperature/position profile.
It is possible to use a temperature sensor (not illustrated) in the
cold inlet 12 to determine the cold temperature. However, an
alternative is to use the temperature measured by temperature
sensor 18 upon start-up. It will be appreciated that most systems,
there will be some dead lag, i.e. a length of fluid in the pipes,
between the hot fluid supply and the mixing valve 2. Hence, upon
start-up, no hot fluid will be mixed with the cold fluid and the
temperature measured by the temperature sensor 18 will be the
temperature of the dead lag of fluid. This temperature will usually
be the ambient temperature of the building in which the system is
installed. This, in turn, will be will be representative of the
cold fluid temperature, though, in practice, will usually be
slightly higher.
In order to further assist in the efficient recognition of an
appropriate characterisation, the control system 6 could measure
the hot fluid temperature in the hot inlet 14. This is not
essential, but could be achieved using a temperature sensor (not
illustrated) in the hot inlet 14. In this way, the control system 6
would know the end points of the temperature profile and could
estimate an appropriate characterisation with only one intermediate
value for valve position versus outlet temperature.
It should be appreciated that the characterisation determined by
the control system 6 is not limited only to the expected non linear
profiles represented in FIG. 4 and discussed above. In particular,
as mentioned above, by monitoring operating conditions of the
apparatus on an ongoing basis, the control system 6 can build up a
representation of any characteristics of any system.
Following on from the above, it will be appreciated that the
characteristics of a system can change with time. For instance, for
a domestic water system after start-up, the temperature of the hot
water at the hot water inlet 14 may increase as the supply pipes
are brought up to the temperature of the hot water. Alternatively,
one of the supplies may be fed from a source which decreases in
pressure as water is used.
The control system 6 may, therefore, monitor and keep a record of
characterisation with respect to time. In this way, the control
system 6 can change the characterisation which it applies to the
system over time following start-up of the fluid flow.
The control system may also choose an appropriate characterisation
according to how long the mixing valve 2 has been in a no-flow
state with both inlets 12,14 shut off. For example, in a domestic
water supply, if the mixing valve 2 has been in a no-flow state for
only 15 minutes, the water and pipes between the hot water source
and the mixing valve 2 will not have cooled to room temperature so
that, upon start-up, the control system 6 can apply a
characterisation more appropriate than the usual. start-up
characterisation.
On the other hand, if the mixing valve 2 is in the no-flow state
for only a very short period of time, for instance 1 minute, then
the control system 6 can assume that the operating conditions of
the apparatus have not changed at all. In this way, the control
system 6 can immediately apply the same characterisation as was
used before the apparatus was shut down
Where the control system does not store separate characterisations
for various types of start-up as discussed above, it is still
possible for it to optimise the start up procedure. In particular,
the control system 6 can mate use of its characterisations for
normal running conditions and/or a record of the position of the
valve 2 immediately before shut down.
When the mixing valve is tuned on again only a short while after
being turned off (for instance, a few minutes), then the input
conditions can be assumed to have not changed. In this situation,
if the demand mix has not changed since last use, the valve 2 can
be driven immediately to the last stable position. Similarly, the
control system 6 can assume that he previous characterisation still
applies and drive the valve immediately to the position appropriate
for the requested mix. In this way, the control system 6 ignores
the current conditions, for instance as indicated by the
temperature sensor 18 and the associated control loop, and returns
control of the valve 2 to the control loop after only a short wait
of for instance about 3 seconds. This gives the fastest possible
start-up time.
Where the mixing valve is turned on again after a long time of
being off, for instance more than a few minutes, then the input
conditions can be assumed to have changed. However, even in these
circumstances, it is still possible to make use of the normal
working characterisation used by the control system 6 to drive the
valve to approximately the right position, i.e. using the learnt
data about the average valve position for a given mix as
represented by the characterisation. In these circumstance the
control loop is restarted after a longer wait, for instance about
20 seconds, or if the mix is detected, for instance by the
temperature sensor 18, to be nearing the demand conditions. Thus,
in the case of a domestic water supply, this ensures a more stable
response in the system when the dead leg in the hot water supply
has passed and hot water first reaches the mixing valve 2. As will
be discussed below, with such an installation, the system can also
incorporate a further safety feature such that, if the temperature
sensor 18 indicates an illegally high temperature the control
system 6 overrides the processes discussed above and drives the
mixing valve 2 to fill cold anyway.
In order to control the valve, the control system 6 may use a PID
controller, since it is flexible enough to provide a stable and
safe response for most conditions. However, it is difficult to
optimise through calculation, simulation or experimentation.
It is possible to deduce all of the plant and system time responses
to a reasonable level of accuracy by experimentation and
approximation to sample time dependent functions, i.e.
experimentation to establish the velocity profiles of the motor.
Therefore it is possible to calculate controller parameters for an
optimum response. By reducing the order of the controller, this
task is made relatively simple.
The integral term can be removed from the controller if the
controller output indicates the positional error rather than the
absolute position. FIG. 5 illustrates an appropriate
arrangement.
To provide the trajectory planner with an absolute position, the
actual position (Pa) needs to be added to the position error (Pe)
to give a demand position (Pd). This local feedback loop will
insure the motor is driven as fast as possible at all times.
The derivative term gives an output proportional to the rate of
change of error. This gives two advantages. Firstly, in response to
sudden temperature errors (eg. water pressure disturbances), the
derivative action will produce a large compensating controller
action Secondly, when the actuator is moving towards the demand
temperature at speed, the derivative term will produce an output to
slow the actuator. In this way, as the derivative term is
increased, the proportional term can also be increased, improving
the controller rise time.
The derivative term is limited primarily by system noise. As the
derivative gain is increased, the noise which contains fast edges
will cause the actuator to `chatter` resulting in unnecessary motor
and gear wear. The proportional gain is mainly limited by the
thermistor time response.
With regard to the adaptive strategy discussed above, the time
constants of the system can be considered fixed so it is only the
instantaneous gain of the plant that is needed to keep the control
loop critically damped. Start-up is also important and data about
the correct position for a given temperature will allow an optimal
start-up response. One limitation is that there is little time to
perform complex mathematical functions on-line. Thus, if these have
taken place they are preferably carried out off-line. The
controller may calculate the new gain value when off in preparation
for the next time the valve is operated. It does this because the
processing overhead to calculate the new gas is quite high. A low
cost microcontroller does not have sufficient processing power to
rum the control algorithms and calculate the new gains at the same
time. When the valve is off, the microcontroller has virtually no
other processing to perform It is proposed that the valve should
operate with 0.1. second cycle during which the algorithm checks
the demand temperature, actual temperature, compares the two and
calculates the error, then knowing the previous error the control
can carry out any adjustment required. Significant processing
speeds would be required to constantly re-calculate the gain values
within the 0.1 second cycles.
According to one embodiment, the plant response is split into 5
temperature bands and within each of these bands a single
temperature/position co-ordinate is stored. This is illustrated in
FIG. 6. The co-ordinate is derived from a running average of stable
points reached in this temperature band. The gain is defined by the
number of actuator steps needed for a 1 degree change in
temperature and is calculated off-line between each of the stored
coordinates. The gain is extrapolated above and below the top and
bottom points. Where no data has been collected a predefined `safe`
gain is used.
With respect to the system of FIG. 5, only the controller (PD or
otherwise) is adaptive and the correct gain is selected for the
current temperature or position. It is defined as being
proportional to the inverse of the plant gain. The constant of
proportionality is tunable.
On start-up, if data has been collected in the same temperature
band as the demand temperature then a demand position is
interpolated from the nearest recorded co-ordinate using the stored
gain. The valve can thus be moved directly to the calculated
position. The system will leave this mode if the demand temperature
is reached or if the demand temperature is changed. The system will
also leave this mode after a predetermined time. This time should
be set slightly longer than the expected cold dead leg time (cold
water in the hot pipe) as it will stop the actuator moving to the
full hot position.
The behaviour of the valve with different external water
connections can be characterised during the design process. This
will yield a graph (FIG. 9) containing a set of curves representing
blended water temperature against valve position. Mathematical
differentiation of these curves will produce a graph of gradients
against valve position (FIG. 10). A new curve representing the
maximum gradient at every position can be derived (FIG. 11). For
the system to operate as fast as possible and to be stable for all
external water connections the maximum controller gain must be
proportional to the inverse of the maximum gradient curve at every
position. In FIG. 11 the maximum controller gain (derived from the
maximum gradient curve) is shown with respect to the actuator
position, it has been averaged to give a smoother curve.
Where the mixing valve apparatus is used to mix hot and cold water
for domestic use, such as for a shower, the temperature of the hot
water at the inlet 14 may be unsafe to be dispensed from the outlet
16. In particular, where the apparatus is to be used by, for
instance, children or the elderly, there may be a danger of the
control panel 8 being set to a temperature which is too high.
It is possible to provide a mechanical stop on the control knob of
a control panel 8 preventing the control knob from being turned
beyond a selectable maximum temperature. Also, it is possible to
include alternative means on the control panel 8 for setting
electronically a maximum selectable temperature. Unfortunately,
these arrangements have the disadvantage that the user may
inadvertently override or change the preselected maximum
temperature and then select a temperature which is too high.
In order to overcome this, as illustrated in FIG. 1, the control
system 6 may, itself be provided with an input 36. Be input 36 is
used to set the maximum temperature which can be selected by the
control panel 8. Once installed, the control system 6 and mixing
valve 2 will be generally inaccessible. Therefore, using the
control panel 8, the user will only be able to select temperatures
up to the maximum temperature selected by the input 36 The input 36
may take any suitable form, for example a slider or rotatable knob
operating for instance a potentiometer or up and down buttons used
in conjunction with a display on the control system 6 itself or on
the control panel 8. In some embodiments, the input 36 could also
be provided by a control which is operable only by a special tool,
for instance a slotted head to be turned by a screwdriver.
In previous arrangements where a preselectable maximum temperature
is provided, there is a disadvantage that only part of the range of
movement of the control knob is ever used. It is now recognised
that it would be advantageous to give always the control knob its
full range of movement, but vary the sensitivity so that its
maximum position corresponds to the preselected maximum
temperature. In other words, the scale used by the control panel 8
is automatically adjusted. This allows optimum use of the control
knob such that with a lower preselected maximum and, hence, small
range, the control knob allows more accurate control of
temperature.
This arrangement is particularly advantageous where the maximum
temperature is set electronically, rather than as a mechanical
stop. In this respect, the scale for the input control of the
control panel 8 can be adjusted to cover only the temperature range
defined by the maximum temperature set by the input 36.
In some arrangements, the control knob may be provided with a
corresponding display scale of unmarked dimensions. For instance,
the display scale may range from "MIN" to "MAX" with a plurality of
divisions in between. However, where the display scale indicates
specific values such as temperatures, it is preferable that the
display is adjusted automatically according to preselection of the
maximum temperature so as to show appropriate values up to the
maximum value.
In a further arrangement means are provided to preselect minimum
temperature. In this case, the control system can adjust the ranges
and display of the control panel 8 accordingly.
FIG. 7(a) illustrates a control panel 8 having a slider 38 for
selecting the desired temperature. The slider 38 may move from a
minimum temperature position to a maximum temperature position 42.
The control system 6 allocates the maximum temperature position 42
to the maximum temperature selected by input 36. In this way, the
full range of movement of the slider 38 is available to select the
desired temperature. Indeed, in normal use, the operator would be
unaware of the maximum temperature setting.
Optionally, a display 44 may be provided to display the selected
temperature.
FIG. 7(b) illustrates a control panel 8 with a similar slider 38
having maximum and maximum temperature positions 40,42. The control
panel 8 is provided with a display 46 providing a representation of
the selectable temperature scale alongside the slider 38. The
display 46 includes segments 48 displaying selectable temperatures.
Hence, the scale represented on the display 46 and the temperatures
indicated in the segments 48 are determined according to the range
of temperatures selectable up to the maximum selected by input 36.
The display 46 may be embodied as an LCD or such like and thereby
easily allow a variety of scales and alphanumeric characters to be
represented.
Of course, it will be appreciated that the same principles may be
applied to other forms of control panel 8, such as those with
rotary knobs.
It is possible for the system to control an external or internal
water pump. This pump is switched on when the valve is opened and
off when the valve is closed. Preferably the pump switch-on is
delayed when the valve is opened. This allows the valve to move
through the cold position before the pump increases the flow rate.
This minimises the unwanted cold water supplied during start
up.
Where a valve, such as illustrated in FIGS. 2 and 3, controls a
flow of fluid by means of a valve servo, there is a problem that,
should there be a power failure whilst operating, the valve will
remain open indefinitely and continue to supply fluid.
As illustrated in FIG. 8, the control system 6 is provided with an
electrical power input 50 and an electrical energy store 52.
Although illustrated as a separate component, the electrical energy
store 52 is preferably embodied as an internal part of the control
system 6 as illustrated in FIG. 1. Thus, during normal operation,
the control system 6 operates under the power of the electrical
power input. However, in the event of a power failure, power is
supplied from the electrical energy store 52. In particular, the
control system 6 makes use of the energy available from the
electrical energy store 52 to operate the valve servo 4 to move the
valve to a closed position, in other words, to shut the valve off
and drive it to a position in which no flow occurs through the
valve.
The electrical energy store 52 is preferably maintained in a
charged state by the electrical power input 50 during normal use.
In other words, the energy store 52 is of a rechargeable
nature.
Rather than use some form of battery, it is proposed to use a
capacitor as the electrical energy store.
Non-rechargeable batteries would obviously need replacing. Compared
to capacitors, rechargeable batteries tend to have a lower energy
density; need a complex charging circuit; and have a more limited
charge/discharge life. They are also of generally low voltage such
that it would be necessary to step up the voltage from about 1.5V
to about 40V in order to drive the motor.
In order that the capacitor can provide sufficient power to operate
the valve, it is preferred that it should be charged to a
relatively high voltage since the energy stored is proportional to
the square of voltage, but only increases linearly with the value
of the capacitor. Ideally, the energy should be stored at the
highest voltage possible.
With a view to safety issues in domestic water installations, it is
preferred that the capacitor is charged to at least 40 volts and
preferably at least 50 volts. For instance, if the energy is stored
on the low voltage side of the transformer, there is a practical
limitation of 42.4V imposed by the relevant safety standards in the
United Kingdom. Hence, in this instance the energy would be stored
at 42.2V. Mains 230V ac could be stepped down to a safe low voltage
through a transformer and then rectified to d.c. In order to store
the energy at a higher voltage, then an alternative approach would
be to use a switched mode power supply solution. Such a system
would require that the incoming 231 Vac mains is rectified to d.c.
and the energy stored at this point. A switched mode power supply
circuit would then be used to translate this down to a safe
isolated d.c. voltage.
In this way, a smaller capacitor may be used for a given energy,
thereby resulting in reduced cost and space.
In the event of a power failure, the control system 6 may estimate
the power required to move the valve to its off position, i.e. with
no flow. This will, of course, vary according to the current
position of the valve. The control system 6 may also estimate the
available amount of electrical energy remaining in the electrical
energy store 52. Thus, the control system 6 may allow the valve
apparatus to continue operating with the selected flow until it
determines that the energy stored in the electrical energy store 52
is approaching the amount required to shut off the valve. Thus, in
the event of a momentary interruption in the power supply, the
control system 6 will not unnecessarily shut off the valve.
In order to minimise the size of electrical energy store 52
required and/or to maximise the time for which the apparatus may
continue to fiction during a power failure, the control system 6
may shut off power to unnecessary parts of the apparatus under its
control. In other words, in the event of a power failure, the
control system 6 may only allow continued supply of power to some
of the components in the overall apparatus. For instance, if the
control panel 8 is provided with a display and/or illumination,
this can be turned off. The control system 6 can be turned off and
the valve actuator will only be operated in response to abnormal
conditions. Similarly, digital communications with the control
panel of other accessories can be turned off.
Of course, preferably, the control system will only allow the flow
to continue provided it remains wit certain limits and not
regardless of inlet conditions.
During normal use of the control system 6 and valve, the valve and
valve servo are used with little consideration of power
consumption, but more concern for optimising speed and control. In
the event of a power failure, the control system 6 may control the
valve servo in a different manner. In particular, it may supply
power to the valve servo in such a way as to optimise movement of
the valve to its off position. In other words, the trajectory of
movement of the valve servo and valve is chosen so as to bring the
valve to its position of no flow using the minimum amount of energy
as possible. Thus the system may operate using he most efficient
motor drive current and the most efficient speed for the motor. The
most efficient mode of the power supply could also be used where,
for instance, a switch mode power supply is used.
It is possible to use a stepper motor as the valve servo. As is
well known, it is possible to operate a stepper motor by half
steps. Thus, it is proposed that, during normal use, in order to
provide maximum control, the stepper motor would-be operated by
half steps. However, in the event of a power failure, the control
system 6 operates the stepper motor by whole steps in order to move
the valve to its off position as quickly and efficiently as
possible.
With some valves, for instance that illustrated in FIGS. 2 and 3,
it is possible that a state of no-flow will be achieved at two
positions of the valve
For the embodiment of FIGS. 2 and 3 when used for supplying a mix
of hot and cold water, the control system 6 may be configured so as
normally to always move the valve to an off position adjacent
maximum cold water supply. In this way, upon starting use of the
apparatus, the user will always be provided with cold water before
hot, thereby avoiding a user from being unnecessarily scalded.
However, the control system could be configured such that, in the
event of a power failure, it moves the valve to the nearest off
position, whether or not his is adjacent the hot or cold water
supply.
Although it is possible for the valve servo 4 to be connected
directly to the valve 2, in order to achieve good control of the
valve 2, movement of the valve servo will often exceed that
required for the valve 2. In other words, a gear train is used
between the valve servo and valve 2. Unfortunately, gear trains of
any type may result in some back lash. In other words, when
reversing the direction of movement of the valve servo 4, the back
lash in the gear train will have to be taken up before movement in
the valve 2 starts.
In the illustrated embodiment, the gear train is formed internally
of the housing of the valve servo 4.
As illustrated in FIG. 1, a sensor 54 may be provided on the valve
2 or at least on a shaft directly connected to the movement of the
valve 2. The control system 6 may then operate a start-up procedure
to determine the back lash in the gear train.
The detector 54 need only detect a single predetermined position of
the valve 2.
The control system 6 then moves the valve servo in one direction by
an amount sufficient to take up any back lash in the gear train and
past the at least one position detected by the detector 54. Having
determined from the detector 54 that the valve 2 has moved past the
predetermined position, the control system 6 then reverses the
direction of the valve servo 4 until the valve 2 once again passes
the position detected by the detector 54. In a perfect system, the
amount by which the valve servo 4 is operated to return the valve 2
to the detected position will be the same as the amount by which it
was moved away. However, in practice, the valve servo 4 will have
to be operated by a greater amount to return the valve 2 to the
detected position. The additional amount by which it is operated
represents the back lash in the gear train.
Having determined the back lash in the gear train, the control
system can then use this information when operating the valve servo
4 to move the valve 2 during normal use. In particular, when the
valve servo 4 is used to move the valve 2 in a direction opposite
to the previous direction of movement, then the control system 6
will operate the valve servo 4 by an additional amount to
compensate for the back lash in the gear train.
In this way, the control system can achieve much greater accuracy
and speed of operation.
In order to provide good sealing operation, valves are constructed
with resilient seals which press against sealing surfaces. For
instance, in the valve illustrated in FIG. 2, the cup seals 22,24
seal against the surface 26 of the valve member 20. When a valve is
not operated for a long period of time, the material making up the
resilient seals may start to adhere to the sealing surface such
that when the valve is next used the resilient seals may be
damaged. Also, the stiction effect of the seals on the disk surface
26 causes the operating torque to rise with time. High stiction
between the seals and the disk surface could cause the valve to jam
in the off position or could have a detrimental effect on the gear
box in the long term.
In-operation may occur for a number of reasons. For instance, where
the apparatus of Figure us used for mixing hot and cold water for a
domestic shower, the shower may be used only occasionally.
It is now recognised that, by operating the valve regularly, the
stiction is prevented from growing unduly. In this regard, the
control system 6 may include a timer and may monitor how long it
has been since the valve 2 was last operated. When the time since
last operation exceeds a predetermined limit, the control system 6
may then operate the valve servo 4 so as to move the valve 2.
Movement of the valve 2 need only be very slight, in particular,
enough only to slide the resilient seal in either direction.
Preferably, the construction of the valve 2 is such that slight
movement is possible in the no-flow state so that the valve and
resilient seals can be moved sufficient to slide the seals without
starting any flow through the valve 2. Of course, even if this is
not possible, the movement will be so small and so quick that
barely any flow will occur through the value 2.
For a domestic shower application, it is common that the valve
would be operated every 24 hours. In this case, the control system
6 should use a predetermined period of more than 24 hours for
automatic movement of the valve 2. For instance, a period of
approximately 30 hours allows for a user to be running slightly
later than normal in his or her daily routine and, in comparison to
a period of approximately 24 hours, would, in those circumstances,
avoid the user hearing the automatic operation. On the other hand,
with a period of approximately 20 hours, where the shower is used
in the morning, it would not be operated until the middle of the
night and, therefore, would not be noticed. Certainly, there is
little need for automatic operation within 12 hours and, in
practice, automatic movement once every week would be
sufficient.
In a control system having a control loop based on the detected mix
conditions, the control loop includes a gain and damping
appropriate to give an optimum response under usual working
conditions. However, it is now recognised that in some
circumstances, such as failure in the installation or fluid supply,
the response of the normal control loop will not be adequate.
Hence, it is proposed that the control system 6 includes a
transient detector control loop 56 independent of the normal
temperature control loop and that it uses this to shut off the
valve 2 during exceptional circumstances.
The control system as discussed above will attempt to minimise the
error between a demand value, e.g. requested temperature, and an
actual plant output value, e.g. measured temperature. However, no
control system can react infinitely fast to changes in input
conditions. It is possible to increase the gain of the feedback
system such that a small change in error causes a large corrective
action. However, this can lead to instability in the control loop
under normal conditions.
It is possible for input conditions to change dramatically and
these instances here are described as transients. In a domestic
shower installation there may be a loss of cold water supply. In
this case, there would be a risk that the normal control loop would
not be able to control the valve sufficiently fast so as to prevent
a slug of pure hot water reaching the user. With a fast temperature
probe and high feedback, it is possible to limit the amount of
temperature over shoot. However, in practice, it is desirable to
use a low-cost controller system and low-cost temperature probes,
e.g. thermistors, which are slower.
It is proposed that a transient detector control loop 56 should be
provided independently of the normal control loop, either as a
separate software routine or as an independent processor within the
control system. Thus, for the arrangement of FIG. 1, unlike the
normal temperature control loop, the transient detector control
loop 56 would continuously monitor the actual temperature, rather
than the demand temperature. It is then arranged so as to predict
what a faster temperature probe would have seen in the system.
In particular, the transient detector 56 works by continuously
monitoring the rate of change in temperature detected by the
temperature sensor. By knowing the time constant of the sensor, the
transient detector 56 can then predict what temperature the device
is actually "seeing". For example, a thermistor might take 0.3
seconds to register 30% of a change in temperature. In this case,
if the transient detector 56 monitors a 4-C change in 0.3 seconds,
it can predict an actual change of 12-C.
If the transient detector 56 detects that a safe time/temperature
profile has been exceeded, it overrides the normal temperature
control loop and forces the control system into a "transient"
state. A profile of acceptable temperatures above the demanded
value with respect to time can be used to trigger the transient
detector if exceeded.
If the transient detector 56 is triggered, there is no attempt to
use the normal temperature control loop, for instance by
dynamically changing the gain. The transient detector 56 suspends
the normal temperature control loop (FIG. 5) takes control of the
valve and causes the valve to be driven immediately to the full
cold or off position. In particular, it ensures that the hot water
is reduced to substantially zero.
Once the detected temperature falls below the demand temperature by
a predetermined threshold, the transient detector 56 may then
relinquish control to the normal temperature control loop
again.
In this way, the normal temperature control loop may be designed
for optimum performance whilst the transient detector 56 provides a
separate safeguard against unwanted transients in the water
supply.
For the arrangement of FIG. 1 used for an ablutionary shower, it is
important that failure does not result in the supply of only hot
water. Hence, it is proposed that the control system 6 also
includes an error detection circuit 58 for detecting errors in the
apparatus and the operation of the system. In particular, it may
then operate a fail-safe mode.
The role of the error detection is to detect whether there is an
abnormal fault condition which may have a safety implication and to
take appropriate action.
The temperature sensor, for instance thermistor, can fail
open-circuit or closed-circuit. If it fails open-circuit, for
instance because a wire becomes detached, the high resistance can
look like a cold temperature and, hence, the control loop will move
the valve to full hot. On the other hand, a short-circuit failure
will look like a very hot temperature and, hence, the valve will
move to full cold.
The normal range of interest would be 15-C to 55-C. Hence, it is
proposed that should the system detect temperatures below or above
these limits, then it will determine that an error has occurred and
turn off the valve.
In one embodiment, a negative temperature coefficient (NTC)
thermistor is used whereby the resistance fall with increasing
temperature. The resistance of the thermistor is converted to a
voltage level via signal conditioning circuitry with this voltage
level being presented to an analogue to digital convertor. The
signal conditioning circuitry can be designed such that the voltage
levels are constrained to the dynamic range of the ADC (eg. 0V to
5V) and designed such that 0V (for example) corresponds to one
extreme of temperature range (for example, the minimum) and 5V (for
example) corresponds to another extreme of temperature (for
example, the maximum) which it is desired to measure. Temperatures
outside of these extremes would be clipped to 0V or 5V
respectively.
The most likely failure is where a thermistor becomes disconnected
and hence the measured resistance appears very large corresponding
to a very low temperature. Such a condition is very hazardous since
the control system, in measuring an apparently low temperature,
would move the valve to the full hot position if the desired set
temperature could not be obtained. By exploiting the fact that the
temperature of the water will never be less than 0 deg C. under
normal operating conditions, this temperature (or less) can be
detected as an illegal temperature and the control system 6
configured to turn the valve off under such conditions. It will
also be recognised that other temperatures can be selected as an
appropriate threshold.
Another common failure is for he thermistor or connecting circuitry
to short circuit such that the resistance appears very small. This
condition can also be detected if the signal conditioning circuitry
is scaled such that the maximum temperature measureable by the ADC
can be known to be a temperature which can never occur under normal
operating conditions. A good example is 100 dec C. in a water
mixing valve. It will be recognised such that other maximum
temperatures can also be selected.
In this way, if the control system detects the illegal states of
0.degree. C. or 100.degree. C. (+/- a tolerance), then an error can
be flagged and the valve turned off.
In another embodiment, two comparators may be used which detect the
illegal states and provide a single bit indication to the control
system.
As discussed above, the selectable maximum temperature control 36
may use a potentiometer to alter the selected maximum temperature.
If the potentiometer were to fail (open circuit or short circuit)
then a previously safe temperature, for instance 35.degree. C.,
could potentially revert to the maximum selectable temperature of
for instance 55.degree. C. By associating the minimum position of
the selectable temperature with zero resistance, then a short
circuit will always fail safe and need not be detected. On the
other hand, by associating the magnum selectable temperature with
the maximum potentiometer resistance, it is possible to detect an
open circuit, for instance by way of an external fixed resistor in
series with the potentiometer.
If the control panel 8 becomes disconnected from the control system
6 during use, this is a potentially hazardous situation. In this
respect, it is proposed that the control system continually checks
for valid signals from the control panel and switches the valve off
if invalid conditions are detected. For analogue control panels,
this requires checking valid signal levels and for digital control
panels, this requires checking that the unit can communicate.
This gives the ability to plug either analogue or digital control
panels or accessories at different times to the same port. The
valve controller can reconfigure itself accordingly. Additionally,
if the control panel or accessory is disconnected, the controller
will detect this and shut down.
As mentioned, the control panel 8 is connected to the control
system 6 by means of a transmission path 10. The transmission path
10 allows the connection of various control panels to the control
system 6. In this regard, the control system 6 is provided with a
control interface. Upon connection of a control panel 8, the
control system 6 may analyse it to determine its type.
The system uses a single input port to support an analogue
electronic control panel and a digital electronic control panel.
The input port has 6 lines and they are configured as shown in
table 1. According to an aspect of the present invention, by
configuring analogue and digital control panels according to these
criteria, the valve system can distinguish between the control
panels and configure itself accordingly. The analogue control panel
uses 2 lines varying between 0V and 5V to represent the demand
temperature and the status of the control panel buttons. The
digital panel uses the I.sup.2 C Acess Buss digital communications
protocol operating at 16 kHz to transfer data about the demand
temperature and button presses. The system has the ability to
identify which of the 2 panel types are connected by inspecting the
signal levels on another line (line 6) on the input port.
Analogue Line Valve Panel Digital Panel 1 1 M pull-up On/Off
indicator N/C 2 Switched 5 V 5 V 5 V 3 1 M pull-down, 10 k Pot with
1 K SDA RC filter and series resistor to 51 R to 1.sup.2 C GND 4 RC
filter and Mode selector SCL 51 R to I.sup.2 C 5 GND GND GND 6 1 M
pull-up Flow indicator 10 k pull-down
The digital communications uses two of the same input port lines as
the analogue panel. The dual function of these lines is allowed by
the configuration shown in FIG. 12. Each electrical valve system
input line is terminated in the same way. The clamp diodes D1 and
D2 protect the terminating circuit from over and under voltage
conditions. C1 and R1 are required by the digital communications.
R2 and C2 provide filtering of the analogue input signals. When the
digital communications are in use R2 prevents the relatively high
capacitance of C2 from disrupting the communications. The presence
of C2 in close proximity to the ADC (analogue to digital converter)
gives added noise immunity to the ADC. The shown values of R2 and
C2 are not specific to the invention, they can be altered to tune
the level of filtering on the analogue signals. It is a requirement
that R2 has high impedance with respect to R1.
The digital protocol allows devices other than a control panel to
communicate with the valve system. This could include pumps, bath
fill systems, hand wasers, extractor fans, lighting systems or
others. The protocol defines a message format shown in table 2.
Byte Meaning 0 Destination Address 1 Source Address 2 Command
Number 3 Payload byte 0 4 Payload byte 1 5 Payload byte 2 6 CRC
High-byte 7 CRC Low byte
There are a number of available commands to allow communication of
system status, temperatures and flows (table3).
Command Function Code MSG_ENQUIRY Report system status 1
MSG_SET_MODE Switch valve on or off 2 MSG_SET_TEMP Set temperature
(in eighths of a degree) 3 MSG_SET_FLOW Switch pump on or off 4
MSG_QUERY_TEMP Report temperature (in eighths of a 5 degree)
MSG_QUERY_FLOW Report pump status 6
* * * * *